Accepting immediately. Always ask for - days to review. Enthusiasm is fine, but immediate acceptance leaves money on the table.
Negotiating only base salary. Equity often makes up -% of TC at L5+. A \50$10$K base increase.
Bluffing about competing offers. Recruiters talk. If you claim a Meta offer at E5 but you interviewed at E4, this will backfire.
Being aggressive or adversarial. Your recruiter is your advocate. They present your case to the compensation committee. Work with them, not against them.